Method and apparatus for a dual mode burner yielding low nox emission

ABSTRACT

A method of operating a burner includes providing supplying a combustible mixture containing a ratio of fuel and air that is incapable of maintaining a stable flame to a combustion chamber. The combustible mixture is ignited by an igniter, and presence of a flame is sensed. The igniter is maintained active to sustain combustion of the combustible mixture within the combustion chamber so that a space exterior to the combustion chamber is heated to a temperature at or above an auto-ignition temperature of the combustible mixture. The temperature of the space exterior is monitored and the combustible mixture is provided at a second flow rate, which is higher than the first flow rate, to extinguish the flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber. When combustion occurs in the space exterior to the combustion chamber, the igniter is deactivated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication No. 61/701,212, filed Sep. 14, 2013, which is incorporatedherein in its entirety by this reference.

BACKGROUND

The use of high velocity gas burners is well known. In such burners,fuel gas and oxidant are mixed with one another and ignited in theinterior of the burner. The resultant hot combustion gases then flow athigh velocity through an outlet and into the furnace chamber for directheating or into a radiant tube for indirect heating. The combustion ofthe fuel gas with an oxidant within the burner results in a greatlyelevated temperature environment in the burner. To increase systemefficiency, the oxidant can be pre-heated to result in highertemperatures. The preheating of the oxidant may be achieved by using arecuperative or regenerative system that uses the residual heat in theexhaust gas. This high temperature combustion environment provides twochallenges. First, the burner internals and combustion chamber areexposed to the very high temperature environment. Second, whencombustion is carried out at extremely high temperatures, thermalnitrogen oxides (NOx) formation is promoted. As combustion temperaturesincrease, the levels of NOx production also increase. In order to dealwith higher combustion temperatures, burners may be constructed fromhigh temperature grade materials, for example, the combustion chamberscan be made of ceramic materials, which can withstand the hightemperature environment. However, the difficulties associated with highNOx emissions still remain unaddressed.

SUMMARY

A method and apparatus for a burner adapted to heat a furnace, radianttube, or other environment of use is described herein. In particular, aburner for providing a fuel gas in combination with an oxidant to effectcontrolled combustion (or oxidation) of the fuel gas in a manner toreduce NOx emissions is described. Combustion of the fuel gas is shiftedfrom within the burner combustor to a location outside the burner oncethe temperature within the furnace/radiant tube has reached a sufficientlevel to complete combustion of the fuel gas.

The burner can provide oxidant and fuel at a ratio and/or velocity thatdoes not permit the burner to maintain a stable flame. Accordingly, theburner can be provided with a stabilization device that is capable ofmaintaining a flame in the burner combustor notwithstanding theinstability created by the oxidant and fuel ratio and/or velocity. Thestabilization device can be turned on or off as desired.

More particularly, the fuel gas may be delivered through a fuel tube fordischarge, such as axial and/or radial discharge, into a burnercombustor for mixing with oxidant at a ratio and/or velocity that is notcapable of maintaining a stable flame. During a start-up stage, thestabilization device is activated, and the fuel gas/oxidant mixture isignited to combust within the burner combustor. The stabilization devicemaintains the flame in the burner combustor. During this period, theflame inside the burner combustor can be monitored with a flame sensor,such as a flame rod or UV scanner.

Once the temperature in the furnace/radiant tube reaches a pre-definedlevel at or above the auto-ignition temperature, the stabilizationdevice can be turned off. When this occurs, flame will be destabilizedand extinguished in the burner combustor such that all combustion willtake place in the furnace chamber/radiant tube, and the flame sensorwill detect a loss of flame inside the combustor. Due to the elevatedtemperature above auto ignition level in the furnace/radiant tube, thismovement of the flame to the furnace/radiant tube space leads tocombustion in the furnace/radiant tube in the absence of a flame in theburner. While the temperature levels within the furnace/radiant tube aresufficient to cause combustion of the fuel gas, these temperature levelsnonetheless are low enough to avoid substantial NOx generation.Moreover, the high exit velocity of the air and fuel providessubstantial blending and recirculation of the furnace/radiant tubeatmosphere with the air/fuel mix, resulting in reduced temperaturespikes formed in the core of the flame jet in the furnace/radiant tube,which are normally experienced during the standard operating mode oftypical burners. After the flame ceases to exist in the burnercombustor, the flow rate of the mixture of fuel gas and oxidant can bemaintained, decreased, or increased, according to the needs of thefurnace operator.

Examples of suitable stabilization devices include a hot surfaceigniter, a continuous spark igniter, a plasma igniter, an arc igniter, abackflow fluid flow, a pilot flame, an electric field generator, amagnetic field generator, and an electromagnetic field generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic views illustrating a burner and control systemfor delivery of fuel gas and combustion air adapted to heat a furnace,radiant tube, or other chamber, in accordance with the disclosure;

FIG. 2 is a fragmentary sectional view of a fuel gas discharge nozzlemounted within a combustor for the burner of FIG. 1;

FIG. 3 is a fragmentary sectional view of the fuel gas discharge nozzleof FIG. 2 taken along line 3-3 in FIG. 4; and

FIG. 4 is a sectional view taken generally along line 4-4 of FIG, 2showing the orientation of an air flow control disk surrounding the fuelgas discharge nozzle of FIG. 2;

FIG. 5 is a diagrammatic view illustrating a first embodiment of astabilization device for the burner of FIG. 1;

FIG. 6 is a diagrammatic view illustrating a second embodiment of astabilization device for the burner of FIG. 1;

FIG. 7 is a diagrammatic view illustrating a third embodiment of astabilization device for the burner of FIG. 1;

FIG. 8 is a diagrammatic view illustrating a fourth embodiment of astabilization device for the burner of FIG. 1;

FIG. 9 is a diagrammatic view illustrating a fifth embodiment of astabilization device for the burner of FIG. 1;

FIG. 10 is a diagrammatic view illustrating a sixth embodiment of astabilization device for the burner of FIG. 1; and

FIG. 11 is a diagrammatic view illustrating a seventh, eighth, and ninthembodiment of a stabilization device for the burner of FIG. 1.

FIG. 12 is a flowchart for a method of operating a burner in accordancewith the disclosure.

Before the embodiments of the burner and method are explained in detail,it is to be understood that the invention is not limited in itsapplication to the details of construction and/or the arrangements ofthe components set forth in the following description or illustrated inthe drawings. Rather, the invention is capable of other embodiments andof being practiced or carried out in various ways. Also, it is to beunderstood that the phraseology and terminology used herein are forpurposes of description only and should not be regarded as limiting. Theuse herein of “including,” “comprising,” and variations thereof is meantto encompass the items listed thereafter and equivalents, as well asadditional items and equivalents thereof.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like elements aredesignated by like reference numbers in the various views. FIGS. 1-4illustrate a burner 10 including a generally hollow tubular cover tube12 having an open end 14 that projects into a furnace/radiant tube 16 orother environment to be heated. By way of example only, the burner 10may project into an enclosed radiant heating tube, or the like, used forindirect heating of a furnace while avoiding substantial introduction ofcombustion products into the furnace. As another example, the burner 10may project into a furnace for direct heating of a furnace withsubstantial introduction of combustion products into the furnace. In theillustrated embodiment, the cover tube 12 is disposed in surroundingrelation to a hollow heat recuperator 18 of ceramic or the like having aconvoluted surface extending outwardly from a housing 20. Therecuperator 18 can surround fuel tube 22, which provides fuel to anozzle assembly 24 disposed within a burner combustion chamber 26 (alsoreferred to as a combustor) located adjacent to the open end 14 of theburner. An annular air passageway 28 can be disposed between the innerwalls of the heat recuperator 18 and outer wall of the fuel tube 22.

As shown, an air supply 30 provides combustion air for delivery from ablower or other supply source (not shown) to the annular air passageway28 for transmittal to the nozzle assembly 24. An oxidant control valve32 is used to control the flow of oxidant. In this regard, the oxidantcontrol valve 32 may be operatively connected to a controller 34 such asa PLC, computer, or the like which opens or closes the oxidant controlvalve 32 in accordance with pre-established commands based on conditionsin the furnace/radiant tube and/or the burner. Likewise, a fuel supply40 provides natural gas or other gaseous fuel for delivery to the fueltubes 21 and 22 for transmittal to the nozzle assembly 24. A fuelcontrol valve 42 is used to control the flow of fuel gas. In thisregard, the fuel control valve 42 may be operatively connected to thecontroller 34, which adjusts fuel feed in accordance withpre-established commands based on conditions in the furnace, radianttube, and/or the burner. It will be appreciated that the fuel gas, airand oxidant can pass into the nozzle assembly in any suitable manner.

A sensor 46, such as a flame sensor, or the like, may be present tocontinuously monitor the presence of a flame within the burnercombustion chamber 26, and to communicate such data to the controller34. As will be described further herein, the controller 34 may utilizethe data from the sensor 46 in combination with temperature data fromthe furnace/radiant tube to control the burner. It will be appreciatedthat the sensor 46 can be any suitable sensor and can be disposed in anysuitable location. In one embodiment, the sensor 46 is embodied as anultra-violet radiation or flame detector 69 that is disposed to sensefor the presence of a flame directly within the combustor chamber 26, asshown in FIG. 5.

Referring now back to FIGS. 2-4, the nozzle assembly 24 can be in theform of a sleeve that is secured about the distal end of the fuel tube22. In this regard, the illustrated nozzle assembly 24 includes aforward nipple portion 50 and a radial disk portion 52 disposed rearward(i.e. upstream) of the nipple portion 50. In this arrangement, theradial disk portion 52 can have a generally concave forward faceprojecting towards the outlet of the burner.

As best seen through joint reference to FIGS. 2 and 4, stand-offs 54 canbe located at positions around the circumference of the radial diskportion 52 to provide centered spacing relative to the surrounding body.This can result in an annular gap 56 (FIG. 5) extending substantiallyaround the perimeter of the radial disk portion 52. The radial diskportion 52 also includes a pattern of interior air passages 58. Duringoperation, oxidant and/or air delivered from the supply 30 may flowthrough the annular gap 56 and the interior air passages 58 towards theburner outlet as shown by the arrows in FIG. 2.

As shown in FIG. 3, the forward nipple portion 50 can include an axialgas passage opening 64 and an arrangement of radial gas passage openings66 aligned with corresponding openings in the fuel tube 22 for outwardconveyance of the fuel gas. During operation, fuel gas can be passedoutwardly from the axial gas passage opening 64 and the radial gaspassage openings 66 and can mix with the oxidant.

The burner 10 may be operated in a flame mode with ignition within theburner combustor or in a flameless mode during which the oxidant andfuel gas combusts only downstream of the combustor outlet in an area 16(FIG. 1), which is external to the combustor, The flameless mode mayalso be referred to as a volume combustion mode, i.e., when combustionis occurring in the volume of the furnace chamber or radiant tube in theabsence of a flame in the combustion chamber 26 of the burner. The flamemode provides the initial start-up of the furnace/radiant tube 16 usingcombustion of fuel gas in the burner combustion chamber 26 to heat upthe furnace/radiant tube. The flame mode can be followed by theflameless mode during which the fuel gas and oxidant are ejected fromthe burner 10 and is allowed to undergo combustion downstream of thecombustor outlet. This dual mode operation results in substantiallyreduced NOx emissions.

Referring again to FIGS. 1-4, by way of example only, and notlimitation, upon initiation of the flame mode, both the air controlvalve 32 and the fuel control valve 42 are set to an open condition thatprovides a flow of oxidant and fuel, which need not be capable ofmaintaining a stable flame within the burner. Unlike previously proposedburners, in which a combustible mixture capable of maintaining a stableflame after initial ignition was required within the burner, in thepresent embodiments, a mixture and/or flow rate of fuel, air and,optionally, the oxidant, may be insufficient to maintain a stable flamewithin the burner during operation in the flame mode. As used herein,oxidant is meant to describe any substance that contains oxygen, such asair, and/or other additives intended to make the combustion of fuel moreefficient and/or to lower emissions.

When combusting in the open condition, air and/or another oxidant willpass along the annular air passageway 28 to the nozzle assembly 24 andfuel gas will pass along the fuel tube 22 to the nozzle assembly 24. Atthe nozzle assembly 24, a portion of the oxidant can flow through theannular gap 56 surrounding the radial disk portion 52, while theremainder of the oxidant can pass through the interior air passages 58.Concurrently, the fuel gas can be expelled from the nozzle assembly 24to mix with the oxidant in the burner combustion chamber 26. As thesematerials mix, a flame stabilization device 90, as shown in FIG. 5, forstabilizing a flame in the burner combustor can be activated to initiatea flame, and remain active to perpetuate the flame as required.

The stabilization device or a suitable igniter, such as a spark rod, hotsurface igniter, direct spark igniter, plasma igniter, electrical arcigniter, field igniter, pilot light igniter, and the like, can beactivated by the controller 34 to ignite the fuel/air mixture in theburner combustion chamber 26 based on, or in response to, a signalprovided by an ultra-violet detector, flame rod, or other type of flamesensor 69 disposed to sense the presence of a flame within the burnercombustion chamber 26, as shown in FIG. 5. This on-demand ignition,which can be activated continuously, can provide stable combustionoccurring in the burner while the flame mode operation is active. Thisflame can be maintained continuously or intermittently, as required, bythe stabilization device until the auto-ignition temperature in thefurnace or in an area outside of the radiant tube is achieved.Throughout the flame mode, thermocouples or other devices cancontinuously monitor the interior temperature of the furnace/radianttube 16 and a flame sensor 69 can monitor the presence or absence offlame inside the burner combustor 26 to provide such data to thecontroller 34 by means of any suitable link.

Once the temperature within the furnace/radiant tube reaches apre-established level (normally about 1550 degrees Fahrenheit orgreater) the controller 34 can communicate with the stabilization deviceto deactivate the stabilization device. The deactivation of thestabilization device causes the flame in the burner combustor 26 to beextinguished when operation transitions to the flameless mode ofoperation of the burner 10. The absence of the flame in the burner canbe detected using the flame sensor (e.g., a flame rod or UV sensor),which can be used as an indication that the flameless mode has beenreached.

During the flameless mode, the fuel gas and oxidant can be passed out ofthe burner 10 without undergoing combustion. Upon entering theauto-ignition temperature furnace/radiant tube environment, the fuel gasand oxidant are raised to a temperature sufficient to activatecombustion without requiring continuous or intermittent ignition.Alternatively, a sustained combustion within the furnace may not requirea combustible mixture to be provided at all through the burner, Thus,the location of the onset of combustion is moved from the burnercombustor 26 downstream to the furnace chamber/radiant tube 16. Due tothe relatively disperse combustion zone outside of the burner 10 and theentrainment of the flue gas within the fuel/oxidant mixture, there isnot a substantial localized temperature spike. NOx production is therebysubstantially reduced. As will be appreciated, once the flamelesscombustion mode has been initiated, the flows of fuel gas and oxidantmay thereafter be cycled on and off, or otherwise maintained, decreased,or increased, to adjust the temperature within the furnace/radiant tubeas desired anywhere above an auto-ignition level.

The stabilization device can be any suitable device that is capable ofmaintaining a flame in the combustion chamber when the flow rate and/orflow mixture of oxidant and fuel gas would otherwise destabilize andeither extinguish, blow out or not otherwise maintain a flame within theburner combustion chamber without the stabilization device. In oneembodiment, shown in FIG. 5, the stabilization device can be a hotsurface igniter 90. The hot surface igniter is a device that useselectrical power in the form of heat provided when an electric currentpasses through an electrical resistive element 92. The resistive element92 is disposed at the end of a rod 94 that extends into the burnerchamber 26 so that the resistive element 92 is adjacent the fuel floworifices of the nozzle assembly 24. The rod 94 may be hollow toaccommodate electrical conduits 96 that interconnect the resistiveelement 92 with appropriate connections to the controller 34. In thisway, the controller 34 can control operation of the hot surface igniter90.

During operation, the resistive element 92 is activated and heated to atemperature that is sufficient to ignite the oxidant/fuel mixture in thecombustion chamber 26. The controller is connected to the hot surfaceigniter to turn it on and off. In operation, the hot surface igniter isturned on to reach a temperature sufficient to ignite the oxidant/fuelmixture, and is left in the on condition to maintain a flame in theburner combustor. Once the furnace/radiant tube has reached the desiredtemperature, the controller can turn off the hot surface igniter todestabilize the flame in the burner combustor and initiate the flamelessmode in the burner combustor, It will be appreciated that the hotsurface igniter can have any suitable shape and size. In addition, thehot surface igniter can be disposed in any suitable position. In oneembodiment, more than one such igniter may be used in the same burnerchamber.

In another embodiment, shown in FIG. 6, the stabilization device can bea direct spark igniter 98. The direct spark igniter 98 is a device thatuses electrical power at a high voltage or that includes a voltagemultiplier coil 100 associated with a spark-producing tip 102 thatprovide electrical arcing that serves to ignite a combustible mixture.The tip 102 is disposed at the end of a rod 104 that extends into theburner chamber 26 so that the tip 102 is generally adjacent the fuelflow orifices of the nozzle assembly 24. The rod 104 may be hollow toaccommodate electrical conduits 105 that interconnect the tip 102 withappropriate connections to the controller 34. In this way, thecontroller 34 can control operation of the direct spark igniter 98.

During operation, the tip 102 is activated to produce an arc that issufficient to ignite the oxidant/fuel mixture in the combustion chamber26. The controller is connected to the direct spark igniter to turn iton and off. In operation, the direct spark igniter is turned on toproduce a spark sufficient to ignite the oxidant/fuel mixture, and isleft in the on condition to maintain a flame in the burner combustor.Once the furnace/radiant tube has reached the desired temperature, thecontroller can turn off the direct spark igniter to destabilize theflame in the burner combustor and initiate the flameless mode in theburner combustor. It will be appreciated that the direct spark ignitercan have any suitable shape, size or configuration. For example, the tip102 need only be disposed within the burner chamber, while the coil 100may be located remotely from the tips at an external location relativeto the burner 10. In addition, the tips can be disposed in any suitableposition, or at multiple positions within the burner chamber. In oneembodiment, more than one such igniter may be used in the same burnerchamber.

In yet another embodiment, shown in FIG. 7, the stabilization device canbe a plasma igniter 106. The plasma igniter 106 is a device that uses anelectrical discharge to produce an arc in a gas disposed between twoelectrodes 108. The electrodes 108 are disposed at the end of a rod 110that extends into the burner chamber 26 so that the electrodes 108 areadjacent the fuel flow orifices of the nozzle assembly 24. The rod 110may be hollow to accommodate electrical conduits 112 that interconnectthe electrodes 108 with appropriate connections to the controller 34. Inthis way, the controller 34 can control operation of the direct sparkigniter 98.

During operation, the electrodes 108 are activated to produce an arcthat is sufficient to ignite the oxidant/fuel mixture in the combustionchamber 26. The controller is connected to the plasma igniter to turn iton and off. In operation, the plasma igniter is turned on to produce anelectrical arc sufficient to ignite the oxidant/fuel mixture, and isleft in the on condition to maintain a flame in the burner combustor.Once the furnace/radiant tube has reached the desired temperature, thecontroller can turn off the plasma igniter to destabilize the flame inthe burner combustor and initiate the flameless mode in the burnercombustor. It will be appreciated that the plasma igniter can have anysuitable shape, size or configuration. For example, the electrodes 108need only be disposed within the burner chamber and controlled remotelyby the controller 34 through an induction coil, capacitor, or otherelectrical device that is disposed within or outside of the burner 10.In addition, the electrodes can be disposed in any suitable position, orat multiple positions within the burner chamber. In one embodiment, morethan one such igniter may be used in the same burner chamber.

In another embodiment, shown in FIG. 8, the stabilization device can bean arc igniter 114. The arc igniter 114 is a device that uses electricalpower to provide electrical arcing that serves to ignite a combustiblemixture. Tips 116, between which the arc is created, are disposed at theend of a rod 118 that extends into the burner chamber 26 so that thetips 116 are adjacent the fuel flow orifices of the nozzle assembly 24.The rod 118 may be hollow to accommodate electrical conduits 120 thatinterconnect the tips 116 with appropriate connections to the controller34. In this way, the controller 34 can control operation of the arcigniter 114.

During operation, the tips 116 are activated to produce an arc that issufficient to ignite the oxidant/fuel mixture in the combustion chamber26. The controller is connected to the arc igniter to turn it on andoff. In operation, the arc igniter is turned on to produce an electricalark or spark sufficient to ignite the oxidant/fuel mixture, and is leftin the on condition to maintain a flame in the burner combustor. Oncethe furnace/radiant tube has reached the desired temperature, thecontroller can turn off the arc igniter to destabilize the flame in theburner combustor and initiate the flameless mode in the burnercombustor. It will be appreciated that the are igniter can have anysuitable shape, size or configuration. For example, the tips 116 needonly be disposed within the burner chamber. In addition, the tips can bedisposed in any suitable position, or at multiple positions within theburner chamber. In one embodiment, more than one such igniter may beused in the same burner chamber.

In another alternative embodiment, a directional secondary airflow maybe provided to the burner chamber 26 to provide a counter-flow of airand/or oxidant in a direction generally toward the nozzle assembly 24and away from the outlet opening 14 of the combustion chamber, as shownin FIG. 9. In this figure, an igniter 90 is used, which can be anyappropriate igniter type operating to ignite a self-sustaining flamewithin the combustion chamber 26 or, alternatively, maintain acontinuous flame within the chamber 26 of an otherwisenon-flame-sustaining mixture. In one embodiment, the secondary air flow200 is provided through one or more openings 202 formed in the sidewallof the hollow heat recuperator 18 in a region overlapping with thecombustion chamber 26. The air entering the combustion chamber 26through each opening 202 is provided, in the illustrated embodiment, bya respective conduit 204 having a valve 206 associated therewith that isresponsive to commands from the controller 34 and operable toselectively fluidly block the conduit 204. In this way, air and/or anoxidant can selectively be provided to the combustion chamber 26. Theconduits 204 are associated with an air source 208 which can be at thesame pressure as the air supply 30 or at a different pressure, forexample, higher pressure, such that a stream of counter-direction aircan be formed within the combustion chamber 26 when the valve(s) 206is/are open.

While the secondary air flow 200 is provided to the combustion chamber,a flame region 210 may be formed in an area where air, oxidant and fuelprovided by the nozzle assembly 24 meets the counter-flowing air fromthe conduits 204. In the illustrated embodiment, the region 210 overlapswith the igniter 90 such that the resulting flame can be sustained moreefficiently within the combustion chamber 26. In operation, thecontroller 34 can open the valve(s) 206 to provide a counter-flow ofoxidant to the oxidant and fuel passing the nozzle assembly. An ignitiondevice, such as a spark, can ignite the oxidant/fuel mixture to create aflame in the combustion chamber. The counter-flow of oxidant canstabilize the flame in the combustion chamber. Once the furnace/radianttube has reached the desired temperature, the controller can close thevalve(s) supplying oxidant to the backward oxidant pathways, which willdestabilize the flame in the burner combustor to initiate the flamelessmode in the burner combustor. It will be appreciated that the flowpathways can have any suitable shape and size. In addition, the flowpathways can be disposed in any suitable position.

In another embodiment, shown in FIG. 10, the stabilization device can bea pilot flame igniter 122. The pilot flame igniter 122 is a device thatmaintains a relatively small flame lit by providing a predetermined andmetered flow of fuel or a fuel/air mixture continuously. The relativelysmall flame, which is commonly referred to as a pilot flame, serves toignite a larger fuel flow during operation. The pilot flame 124 isdisposed at the end of a fuel conduit 126 that extends into the burnerchamber 26 so that the pilot flame 124 is adjacent the fuel floworifices of the nozzle assembly 24. Flow of pilot fuel in the conduit126 may be controlled by a valve 128, and also ignition of the pilotflame 124 periodically may be accomplished by an igniter 129.

During operation, the pilot flame 124 is continuously kept lit to ignitethe oxidant/fuel mixture in the combustion chamber 26. In operation, thepilot flame is turned on to produce a flame sufficient to ignite theoxidant/fuel mixture, and is left in the on condition to maintain aflame in the burner combustor. Once the furnace/radiant tube has reachedthe desired temperature, the controller can turn off the pilot flame or,alternatively, leave it on but otherwise increase the flow of fuel, airand oxidant to push the flame outside of the combustion chamber andinitiate the flameless mode in the burner combustor. In other words, theincreased velocity of the fuel and air may prevent the dwell of theflame within the combustion chamber, In such condition, the fuel for thepilot flame, which represents a very small portion of the fuel providedby the nozzle assembly 24, may be carried with the remaining fluids andcombust outside of the combustion chamber 26. It will be appreciatedthat the pilot flame igniter can have any suitable shape, size orconfiguration. For example, the pilot flame 124 need only be disposedwithin the burner chamber. In addition, the pilot flame can be disposedin any suitable position, or at multiple positions within the burnerchamber. In one embodiment, more than one pilot flame may be used in thesame burner chamber.

In another embodiment, shown in FIG. 11, the stabilization device can bean electric, magnetic or electromagnetic field generator igniter 130that produces an induction heating effect on a heater element, which canreach a temperature sufficient for ignition of a combustible mixture.The induction igniter 130 can be a device that uses a process forheating an electrically conductive material such as a metal byelectromagnetic induction, where so-called eddy currents in alternatingdirections are generated within the material, whose electricalresistance causes heating of the material. Heat may also be generated bymagnetic hysteresis losses in materials that have significant relativepermeability. A heated tip 132 of the induction igniter is disposed atthe end of a rod 134 that extends into the burner chamber 26 so that thetip 132 is adjacent the fuel flow orifices of the nozzle assembly 24.The rod 134 may be hollow to accommodate electrical conduits 136 thatinterconnect the tip 132 with appropriate connections to the controller34. In this way, the controller 34 can control operation of theinduction igniter 130.

During operation, the tip 132 is heated to a temperature sufficient toinitiate combustion of the oxidant/fuel mixture in the combustionchamber 26. The controller is connected to the induction igniter to turnit on and off. In operation, the induction igniter is turned on toproduce in the heated element a temperature sufficient to ignite theoxidant/fuel mixture, and is left in the on condition to maintain aflame in the burner combustor. Once the furnace/radiant tube has reachedthe desired temperature, the controller can turn off the inductionigniter to destabilize the flame in the burner combustor and initiatethe flameless mode in the burner combustor. It will be appreciated thatthe induction igniter can have any suitable shape, size orconfiguration. For example, the tip 132 need only be disposed within theburner chamber. In addition, the tips can be disposed in any suitableposition, or at multiple positions within the burner chamber. In oneembodiment, more than one such igniter may be used in the same burnerchamber.

A flowchart for a method of operating a burner in accordance with thedisclosure is shown in FIG. 12. When the burner is turned on, an igniteris activated at 301, and a combustible mixture is provided to aninternal burner chamber at 302. In one embodiment, the combustiblemixture forms within the burner chamber as streams of fuel, air and/oran oxidant are provided to the chamber and mix. Unlike past burnerdesigns, the combustible mixture need not be capable of self-sustaininga flame within the burner chamber in the absence of a sustained ignitionsource, which operates to stabilize the flame within the combustionchamber. The presence of a flame is sensed at 304, and a determinationof presence of a flame within the burner chamber is made at 306. At apositive flame determination, i.e., when a flame is detected in thecombustion chamber, a temperature external to the burner is sensed at308. The external temperature is compared to an auto-ignitiontemperature threshold at 310 and, when the auto-ignition temperature isreached or exceeded, the flow rates of fuel, air and/or oxidant may bealtered to transition the flame outside of the burner chamber, orextinguish the flame altogether.

In one embodiment, the burner is configured to maintain flame within theburner chamber by continuously monitoring for presence of a flame whilethe external temperature is below the auto-ignition threshold, and tomaintain an igniter in an active state as a form of flame stabilizer foran otherwise unstable flame. In the event no flame is detected at thedetermination 306, the system is shut-down and restarted bydiscontinuing the flow of combustible mixture at 314, ensuring theigniter is active at 301, and providing the combustible mixture at 302.The igniter is maintained in an active state continuously while thetemperature is below the predetermined value for as long as a stableflame is desired. When the external temperature has been exceeded, theigniter is turned off at 316 to extinguish the flame or to transitionthe flame to an area external to the burner. Following the flametransition or extinction, the flame sensor is interrogated to ensure noflame is present or remains within the burner chamber at 317. When noflame is present, the process ends. However, when a flame is stillpresent in the burner chamber after deactivation of the igniter, theflow rate of the combustible mixture may be incrementally increased ordecreased at 318 to destabilize the flame present and to push the flameoutside of the burner until the flame is no longer present.Alternatively, the system is shut-down and restarted, for example, aspreviously described, by restarting the igniter and restarting thecombustible mixture supply.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein,

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A method of operating a burner, comprising:providing a combustion chamber in the burner, which is adapted toreceive at least a fuel stream and an air stream; activating an igniterwithin the combustion chamber; supplying a combustible mixturecontaining a ratio of fuel and air to the combustion chamber at a firstflow rate, the combustible mixture being incapable of maintaining astable flame; igniting a flame in the combustible mixture in thecombustion chamber by activating an igniter; sensing a flame presencewithin the combustion chamber; maintaining the igniter active tostabilize the flame within the combustion chamber; heating a spaceexterior to the combustion chamber to a temperature at or above anauto-ignition temperature of the combustible mixture; monitoring thetemperature of the space exterior; and deactivating the igniter todestabilize the flame in the combustion chamber such that combustionoccurs in the space exterior to the combustion chamber when thetemperature of the space exterior is at or above the auto-ignitiontemperature.
 2. The method of claim 1, further comprising providing asecondary air stream, which represents at least a portion of the airstream, to the combustion chamber in a direction disposed at an anglerelative to a flow direction of the fuel stream.
 3. The method of claim2, wherein the secondary air stream is provided through at least oneopening formed in a sidewall of a hollow body that defines thecombustion chamber.
 4. The method of claim 2, further comprising forminga flame region within the combustion chamber in an area where thesecondary air stream and the fuel stream meet and overlap with theigniter.
 5. The method of claim 2, wherein the secondary air stream anda remaining portion of the air stream are provided at differentpressures.
 6. The method of claim 2, further comprising selectivelyadjusting a flow rate of the secondary air stream.
 7. The method ofclaim 1, wherein the igniter is one of a hot surface igniter, a directspark igniter, a plasma igniter, an arc igniter, a pilot flame igniter,or an electric, magnetic or electromagnetic field generator igniter. 8.The method of claim 1, wherein the space exterior to the combustionchamber is a furnace chamber in a furnace, and wherein the spaceexterior to the combustion chamber is a radiant tube disposed in thefurnace chamber.
 9. The method of claim 1, wherein a controllerautomatically adjusts at least one of a flow rate of the fuel stream, aflow rate of the air stream, and a flow rate of an oxidant stream, whichoxidant stream is included in the combustible mixture, based on signalsprovided to the controller that are indicative of the sensing of theflame presence and the monitoring of the temperature of the spaceexterior,
 10. The method of claim 1, wherein the burner furthercomprises a nozzle for the fuel and air streams to pass through andintermix in the combustion chamber.
 11. A method of operating a burner,comprising: activating an igniter; providing a fuel stream, a first airstream, and a secondary air stream to a combustion chamber of theburner; intermixing the fuel, first and secondary air streams to form acombustible mixture at a first flow rate, said combustible mixture beingincapable of maintaining a stable flame within the combustion chamber;igniting the combustible mixture in the combustion chamber with theigniter; sensing a flame presence within the combustion chamber;maintaining the igniter active to sustain combustion of the combustiblemixture within the combustion chamber; heating a space exterior to thecombustion chamber to a temperature at or above an auto-ignitiontemperature of the combustible mixture; monitoring the temperature ofthe space exterior; providing the combustible mixture at a second flowrate, which is higher than the first flow rate, to extinguish a flame inthe combustion chamber such that combustion occurs in the space exteriorto the combustion chamber; and when combustion occurs in the spaceexterior to the combustion chamber, deactivating the igniter anddiscontinuing the secondary air stream.
 12. The method of claim 11,further comprising providing the secondary air stream to the combustionchamber in a direction disposed at an angle relative to a flow directionof the fuel stream.
 13. The method of claim 12, wherein the secondaryair stream is provided through at least one opening formed in a sidewallof a hollow body that defines the combustion chamber, wherein the burnerfurther comprises a nozzle for the fuel and air streams to pass throughand intermix in the combustion chamber, and wherein the at least oneopening is different than nozzle openings provided for the fuel andfirst air streams.
 14. The method of claim 11, further comprisingforming a flame region within the combustion chamber in an area wherethe secondary air stream and the fuel stream meet and overlap with theigniter.
 15. The method of claim 11, wherein the first and secondary airstreams are provided at different pressures.
 16. The method of claim 11,further comprising selectively adjusting a flow rate of the secondaryair stream,
 17. The method of claim 11, wherein the igniter is one of ahot surface igniter, a direct spark igniter, a plasma igniter, an arcigniter, a pilot flame igniter, or an electric, magnetic orelectromagnetic field generator igniter.
 18. The method of claim 11,wherein the space exterior to the combustion chamber is a furnacechamber in a furnace, and wherein the space exterior to the combustionchamber is a radiant tube disposed in the furnace chamber.
 19. Themethod of claim 11, wherein a controller automatically adjusts at leastone of a flow rate of the fuel stream, a flow rate of the first airstream, and a flow rate of an oxidant stream, which oxidant stream isincluded in the combustible mixture, based on signals provided to thecontroller that are indicative of the sensing of the flame presence andthe monitoring of the temperature of the space exterior.
 20. A methodfor operating a burner, comprising: activating an igniter; providing acombustible mixture to a combustion chamber; sensing a flame presence inthe combustion chamber; maintaining activation of the igniter tostabilize a flame in the combustible mixture within the combustionchamber; sensing an external temperature when a flame is sensed in thecombustion chamber; comparing the external temperature with anauto-ignition temperature of the combustible mixture; and, when theexternal temperature is greater or equal than the auto-ignitiontemperature, transitioning the flame from the combustion chamber to anarea external to the combustion chamber; and deactivating the igniter.